The R-value of human skin varies depending on temperature, but it's approximately 0.72 above a certain breakpoint and 0.13 below that breakpoint. This variation is due to changes in blood flow and other physiological responses.
In simpler terms, R-value measures thermal resistance, or how well a material resists the flow of heat. A higher R-value indicates better insulation. The R-value of skin isn't fixed because our bodies actively regulate temperature.
Here's a breakdown:
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Higher Temperature R-value (approx. 0.72): When the body is trying to conserve heat, blood vessels near the skin surface constrict. This reduces blood flow and increases the skin's resistance to heat loss, resulting in a higher R-value.
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Lower Temperature R-value (approx. 0.13): When the body is trying to dissipate heat, blood vessels near the skin surface dilate. This increases blood flow and reduces the skin's resistance to heat loss, resulting in a lower R-value.
The exact breakpoint temperature for these changes varies depending on factors such as individual metabolism, acclimatization, and activity level. The R-value is also influenced by factors such as skin thickness, hydration, and the presence of hair.
It's important to note that these R-values are relatively low compared to common building insulation materials. For example, fiberglass insulation can have an R-value of 3 to 4 per inch of thickness. This demonstrates that human skin isn't a particularly effective insulator on its own and requires clothing or other external insulation to maintain a comfortable body temperature in cold environments.
